The present invention relates generally to semiconductor integrated circuits, and more particularly to charge pumps.
System designs are routinely constrained by a limited number of readily available power supply voltages (Vcc). For example, consider a portable computer system powered by a conventional battery having a limited power supply voltage. For proper operation, different components of the system, such as display, processor, and memory components employ diverse technologies which require power to be supplied at various operating voltages. Components often require operating voltages of a greater magnitude than the power supply voltage and, in other cases, a voltage of reverse polarity. The design of a system, therefore, includes power conversion circuitry to efficiently develop the required operating voltages. One such power conversion circuit is known as a charge pump. Charge pumps have been used as on-chip voltage generators capable of providing a voltage more positive than the most positive external supply or more negative than the most negative external supply. The demand for highly efficient and reliable charge pump circuits has increased with the increasing number of applications utilizing battery powered systems, such as notebook computers, portable telephones, security devices, battery-backed data storage devices remote controls, instrumentation, and patient monitors, to name a few.
Inefficiencies in conventional charge pumps lead to reduced system capability and lower system performance in both battery and non-battery operated systems. Inefficiency can adversely affect system capabilities e.g., limited battery life, excess heat generation and high operating costs. Examples of lower system performance include low speed operation, excessive operating delays, loss of data, limited communication range, and inability to operate over wide variations in ambient conditions including ambient light level and temperature.
Charge pumps utilize a pass device or gating device to connect the higher amplitude voltage to an output of the charge pump after the charge pump has accumulated or built-up sufficient charge to provide the desired voltage level and polarity. The pass device may be an N-well or P-well field effect transistor (FET) formed in a substrate of material of different conductivity. Accordingly, the N-well or P-well will form a P-N junction with the substrate. If this P-N junction becomes forward biased, a latch-up condition can occur and the pass device or gating device can be damaged or destroyed and the charge pump rendered non-operational.
Accordingly, there is a need for a charge pump that can operate efficiently and is not subject to a latch-up condition.
In accordance with the present invention, a charge pump for providing a higher output voltage relative to an input or supply voltage includes a charge storage device or main pump capacitor. A pre-charge circuit is included for pre-charging the charge storage device to a charge level to provide a predetermined output voltage from the charge pump. A pass device is coupled between the charge storage device and an output of the charge pump. A circuit is coupled to the pass device to prevent latch-up of the pass device.
In another embodiment of the present invention, an electronic system includes at least one component operating at a predetermined voltage higher or more negative than a supply voltage. A charge pump is coupled to the at least one component to generate the predetermined voltage and includes a charge storage device or main pump capacitor. A pre-charge circuit is provided to pre-charge the charge storage device to provide the predetermined voltage and a pass device is provided to connect the charge storage device to an output of the charge pump. The charge pump further includes a circuit to prevent a well of the pass device from being forward biased.
In accordance with another embodiment of the present invention, a method for making a charge pump includes forming a charge storage device; forming a pre-charge circuit for charging the charge storage device to a charge level to provide a predetermined output voltage from the charge pump; forming a pass device to connect the charge storage device to an output of the charge pump; and forming a circuit to prevent a latch-up condition of the pass device.
In accordance with a further embodiment of the present invention, a method for generating a predetermined voltage higher than a supply voltage includes generating a plurality of signals; boosting a charge level of a charge storage device in response to the plurality of signals; outputting the predetermined voltage when the charge level of the charge storage device reaches a predetermined level; and preventing a latch-up condition.
These and other embodiments, aspects, advantages and features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims.